1. Field of the Invention
The present invention relates to a method and apparatus for testing the water hammer strength of glass bottles using a single glass bottle.
2. Description of the Related Art
The water-hammer-strength test of glass bottles is defined by the “water-hammer test method” prescribed by the Japan Glass Bottle Association. This defines the water-hammer test method for glass bottles serving as packaged items. FIG. 11 is a schematic diagram showing the test according to the above-mentioned definition. In this test, a drop testing machine 15 defined by “JIS Z 0202” is used. A case of lower dummies 18 (the same as samples 19) is placed on a drop surface 16 (an iron plate having a thickness of 20 mm or more), and a case of the samples 19 is disposed thereon. A case of upper dummies 20 (the same as the samples) is placed on a sample stage 17 of the drop testing machine 15. The lower dummies 18, the samples 19, and the upper dummies 20 are bottles filled with a predetermined amount of formal content by a formal filling method and fitted with predetermined caps, or other equivalents, that are packaged in a predetermined manner. The cases hold many glass bottles. The sample stage is set to a predetermined drop height (the distance between the bottom surfaces of the upper dummies 20 and the top surfaces of the samples 19). For example, at first, the upper dummies 20 are dropped onto the samples 19 from a drop height of 30 cm. Then, the drop height is increased by an increment of 5 cm (when the drop height is 60 cm or more, the drop height is increased by an increment of 10 cm) to test whether or not the sample glass bottles, even one of them, are damaged. The drop tests are repeatedly performed up to a predetermined drop height, and the drop height at the time when the sample bottles, even one of them, are damaged is regarded as the water hammer strength.
When the upper dummies 20 are dropped onto the samples 19, the case of the lower dummies 18 is deformed, and the glass bottles of the samples 19 are rapidly pushed downward. However, the content (liquid) in the glass bottles remains at the original position due to inertia, creating vacuum portions at the bottoms in the bottles. Immediately thereafter, the content rapidly drops onto the bottoms, which are in vacuum, causing a water hammer effect.
Packaged-items drop test apparatuses are also disclosed in Japanese Unexamined Patent Applications Publication Nos. 61-147129 and 62-263435.
The “water-hammer test method” prescribed by Japan Glass Bottle Association is not for testing the water hammer strength of the glass bottles themselves, but for measuring the water hammer strength of packaged glass bottles (the water hammer strength varies depending on the specification of the package). Furthermore, because the test cannot be performed without preparing cartons, the test requires many products (about 10 cases). Thus, the water hammer strength of bottle parisons cannot be evaluated during test production in the design phase. Moreover, the test requires considerable labor for tasks such as lifting the cartons, checking the bottles for damage, cleaning up of the damaged bottles, checking the cartons for damage, etc.